U.S. fertility trends and levels have become an anomaly, both theoretically and in contrast with what has happened in other developed countries. We argue that one key to understanding this American puzzle lies in understanding fertility trends (overall and age/parity specific) by education and race/ethnicity. To do so, we need fertility rates dis-aggregated by race/ethnicity and education, but unfortunately there is suggestive evidence that the educational and race/ethnicity rates estimated from registration system data are biased. We propose, in seven integrated specific aims, to systematically examine the biases present in vital registration natality data, and then, using other data sources, conduct theoretically guided descriptive analyses of recent U.S. fertility trends and differentials. Specifically, we: 1) Examine the strengths and weaknesses of vital registration data for basic description of U.S. fertility trends and differentials. 2) Estimate age-period-cohort effects on parity-specific fertility time series for the 20th century. 3) Assess the assumptions and usefulness of the Bongaarts and Feeney (1998) technique for decomposing U.S. period fertility differences into quantum and tempo components. 4) Examine parallel or divergent racial/ethnic changes in period fertility. 5) Assess differential change in period fertility by education. 6) Test whether the effects of sex of previous children on subsequent fertility persist over time and are pervasive across race/ethnic and educational groups. 7) Compare these behavioral patterns with stated intentions for additional children.